This invention relates generally to the field of recycling solid waste materials, and more particularly to an apparatus for processing rubber vehicle tires, effecting a separation of the various constituent materials comprising such tires, facilitating reclamation and recycling of said materials.
It has been estimated that up to 8 billion scrap rubber tires lie throughout the United States waiting for a suitable method for disposal while approximately 250 million new tires are added to the stream of commerce every year, ultimately requiring disposal. Environmentally safe tire disposal has thus become a major concern in the national effort for improved environmental quality. The problem has reached such a level that special taxes for research into disposal methods have been imposed, and special funds have been earmarked for research into environmentally-friendly tire disposal methods (such as the California Tire Grant Program).
Faced with a problem of this magnitude and this importance, many methods for tire disposal have been investigated, and are still under investigation. Many of the methods begin with mechanical shredding of the tire such as described in the patents of Moore U.S. Pat. No. 4,813,614 and Granite U.S. Pat. No. 4,015,782. Thin jets of high pressure water have been used by Tugov (USSR patent 213,339) to cut the tire into fragments. All such methods suffer from the same basic drawback: that is, having incurred the time and cost of fragmenting the whole tire, what is to be done with the fragments? Recent practice has been to bury the fragments in a landfill. Shredding prior to burial is advantageous only in that it reduces the free volume required to bury each tire, thereby conserving landfill. This is a short-term solution at best and will shortly be ended by legislation.
Burial in landfills is becoming increasingly difficult as landfills are closed and acceptable sites for new landfills become harder to locate. Also, the problem of malicious or accidental fires involving large accumulations of scrap tires is a serious concern to communities, leading to increased pressures for an effective solution to the tire disposal problem. The problem of disposing scrap tires is becoming such a concern that legislation is under consideration requiring tire vendors to demonstrate acceptable disposal means for each new tire placed into the stream of commerce.
Combustion is another method of tire disposal, either with or without prior shredding. The smoke and soot generated by tire combustion must obviously be controlled, but this seems to be possible with present technology. Finely shredded rubber from scrap tires (often called "granulite" or "crumb rubber") has been used as a fuel source commonly known as "tire derived fuel". Such fuel has been used as an energy source in the generation of electricity, in the production of paper and cement, and in various other industries. Apparently, such burning of suitably fragmented tires (or occasionally whole tires) can be performed in an environmentally safe manner if proper precautions are taken. However, use as a fuel is not the highest and best use of the crumb rubber obtainable from a scrap tire; the recovery value of scrap steel in the tire is lost entirely; and the ash-encrusted steel must still de disposed of, typically in a landfill.
Recycled rubber from tires can also be used as a component of various products commonly known as "tire derived products". Such products include asphalt paving mixtures and as extenders in a variety of rubber products such as roofing materials, walk pads, carpet and flooring underlay and other products. More such products are being demonstrated as time goes on.
Tires typically consist of a reinforcing cord (often steel cord in modern tires), woven typically into a mat, and circumferentially surrounding the tire beneath the road-contacting surface of the tread. A primary purpose of this cord is to strengthen the tire against damage from puncture or impact with holes or road debris. Modern steel cording is typically a rather high quality steel.
Tires also typically contain several heavy metal bands or wires imbedded in the rubber for support on the inner circumference of the tire, where the tire contacts the rim of the wheel. This "bead" is typically a very strong and heavy steel, difficult to shred in many mechanical shredders or causing excessive wear on the shredding devices.
In addition to cord and bead, tires also typically consist of several layers of synthetic or naturally-occurring products arranged into tread, various other plies, sidewalls, inner lining, etc. The precise composition and configuration will typically vary considerably, depending on the type of tire, its intended use and service life, desired market price, and consumer preferences. Such "rubber-like" materials may have a variety of different chemical compositions, and be arranged in differing physical configurations for each tire type, manufacturer, etc. For convenience, we will use the term "rubber" to denote all such rubber-like materials comprising vehicle tires.
Additional support and cohesion is introduced into many tires by using a fabric cord (typically nylon or rayon) imbedded in the rubber and typically located in regions of the tire not contacting the road.
Thus, for purposes of this description, we identify four components of typical vehicle tires: 1) steel cords, 2) bead 3) fabric (or non-metallic) cords, 4) rubber.
Rubber and fabric cord can typically be burned as tire derived fuel, or used in other tire derived products (occasionally following further separation and/or processing). The steel cords and beading will typically have some values as scrap metal, if separated in a resonably clean state. Obtaining effective separation of the various components of a tire in a form suitable for reuse or combustion as a fuel, such that no part of a scrap tire must end its life in a landfill, is a major objective of the present invention.
Mechanical shredding is one method in use today for reducing tires prior to burial in landfills or prior to combustion. However, mechanical shredding typically does not separate the steel cords (or other cording materials) from the shredded rubber tire. Therefore, the shredded rubber is rendered useless for many additional purposes. The economic value of the scrap steel is effectively lost. Following combustion of the rubber/steel, the surface of the steel is typically too encrusted with ash and combustion by-products to make separation and recovery economically worthwhile.
In addition, typical mechanical shredding operations produce particles of rubber scrap generally too large for convenient use as a fuel or as an additive in asphalt paving. Further processing, adding to the costs, would be required to derive economic benefit from reuse of such component materials (although the patent of B. H. Granite U.S. Pat. No. 4,015,782 addresses this problem).
Wear on mechanical shredding devices is a serious concern. For this reason larger tires, such as truck or tractor, are typically not recycled. Also, even for passenger car tires, the heavy steel bead can often produce unacceptable wear on shredders. It is often recommended that tires be "debeaded" before shredding (i.e., physically cut and remove the bead and immediately surrounding rubber from the rest of the tire). Clearly, such debeading adds to the cost of tire recycling and leaves the bead and attached rubber to be disposed of in an acceptable manner.
Efforts to ease such problems of shredding have included the use of cryogenic fluids (liquid nitrogen) to crystallize tires into brittle matter, allowing fragmentation by mechanical crushing (U.S. Pat. No. 4,813,614). The economic advantages of using liquid nitrogen to dispose of garbage have yet to be demonstrated.
Prior work by the present inventor (U.S. Pat. No. 5,115,983; hereinafter "'983") describes a process for using jets of high pressure water (or similar fluid perhaps containing abrasive additives), directed in such manner and under such pressures, to shred the rubber from a tire. The '983 process shreds the rubber into the effluent stream of water, while leaving clean steel behind. This '983 water process naturally separates the crumb rubber from the steel in a single step, allowing the steel to be bundled for resale and recycling, while (typically following drying and screening for size separation) the crumb rubber is in a form suitable for numerous uses in addition to use as a fuel. The advantages the '983 separation process are described more completely in the referenced patent.
The present invention consists of an apparatus using at least one rotating nozzle to direct the jets of water onto all portions of a tire, thereby performing the '983 process in a single step. The present apparatus is capable of separating rubber from the steel contained in a tire, flushing the rubber away from the steel while leaving clean steel behind. Obvious modifications of the present apparatus allow the recycling of tires of various sizes (passenger car, truck etc.) and the processing of previously shredded tires.